T-Rex fossil yields clues to evolutionary puzzle:
study
AFP
CHICAGO, April 12, 2007 (AFP) - US researchers have identified microscopic traces of soft tissue taken from a 68 million-year-old T-rex fossil in a startling discovery that is yielding clues to evolutionary links between dinosaurs and birds, a study released Thursday said.
The tiny protein fragments were extracted from the leg bone of a Tyrannosaurus rex that was discovered in the western state of Montana in 2003, but it wasn't until recently that scientists were able to definitively identify them as traces of prehistoric dinosaur collagen.
The collagen should have degraded millions of years before according to conventional wisdom, but paleontologists at North Carolina State University were fairly confident that what they had was the "barely detectable" remains of dinosaur soft tissue based on their chemical and molecular analyses.
However, they could not definitively say that, so they turned to biochemist John Asara at Beth Israel Deaconess Medical School in Boston to make that determination.
It took Asara a year and a half, but he was finally able to sequence the amino acids in the collagen proteins - a proxy for DNA analysis - and conclude that the T-rex femur did indeed contain traces of collagen, a fibrous protein found in bone.
When the researchers compared those amino acid sequences to those of similar proteins in several contemporary animals, they found that the T-rex sequence had similarities to those of chickens, and to a lesser extent frogs and newts. That finding bolsters a recent and controversial proposal that birds and dinosaurs are evolutionarily related, and change that hypothesis to a theory, the researchers said.
"Most people believe that birds evolved from dinosaurs, but that's all based on the architecture of the bones," said John Asara, who is director of mass spectrometry at Beth Israel Deaconess Medical School.
"This allows you to get the chance to say Wait, they really are related because their sequences are related.' We didn't get enough sequences to definitively say that, but what sequences we got support that idea."
More broadly, the discovery challenges long-held assumptions about the process of fossilization, which in turn opens up new avenues of investigation in the field, the researchers said.
Until now it was assumed that organic matter such as proteins could not survive past a million years, but this discovery shows that ancient proteins can provide genetic clues to organisms that are millions and millions of years old even if they are only marginally viable as they were in this case.
"For centuries, it was believed that the process of fossilization destroyed any original material, consequently no one looked carefully at really old bones," said Mary Schweitzer, an assistant professor of paleontology at North Carolina State University in Raleigh, and one of several researchers who worked on the project. But if molecular data from fossils can be retrieved and analyzed, it may be able to verify current ideas about relationships between fossil and living organisms and between groups of distinct organisms that have no modern descendants.
"This interplay between the fossil record and the molecular record is going to become more and more useful in understanding both ends of the evolution of life on this planet," she told journalists on a teleconference.
"It's really exciting." On a more practical level, the findings will probably change the way paleontologists view and treat future fossils, said Lewis Cantley, professor of systems biology at Harvard School of Medicine.
"I think what this says is that when people make new discoveries now, if they want to get maximum information out, they have to immediately handle material in a way that first of all will avoid contamination and second, ensure that whatever is there gets well preserved because it can be interrogated."
Inevitably, a lot will depend on the condition of the fossil. This fossil was preserved in sandstone 60 feet below the ground and the porosity of the sandstone may have been a factor in the survival of these soft tissues, the researchers said.
Even so, it took the biochemists on the team a year and a half to sequence the amino acids in the proteins using highly sensitive mass spectrometry techniques that first broke the proteins down into fragments of 10 to 20 amino acids and then configured them into a sequence.
The study is published in the journal Science and was a collaborative effort between Schweitzer, Cantley and Asara, and Jack Horner, Regents Professor of Paleontology at Montana State University, who provided the fossil.
